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Large fluctuations in coolant temp any idea why?

('98-'00)
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2.6K views 11 replies 4 participants last post by  adc  
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#1 ·
Just picked up this subaru used and I have been doing more and more maintenance when I have the time. I popped the coolant reservoir cap and it looked like syrup. So I decided to flush since I have taken care of all the other fluids.

So I flush the coolant out, get new coolant in it and the temperature was doing some weird fluctuating but it was come and go. So I popped the cap again and the coolant looked just as bad before so I decided to flush it again and see if maybe there was air in it.

After I got all the old coolant out it made the problem worse, this time the car constantly wanted to overheat. When the coolant temp started to get close to the red, the heater started blowing cold. As soon as I start decelerating I can see the temp gauge go down and once I come to a stop it drops down to a normal temp almost instantly.

Did some reading, I saw others with this problem and it seemed to be the thermostat. I replaced the thermostat and the radiator cap and it has made absolutely no difference. I thought it was fixed, but when I was driving home earlier I realized the heater was blowing cold and it was nearly in the red again.

I bled the system for 30 min, but it seems like the issue is an air bubble in the system. Any idea how I can get rid of it, or does anyone know what my problem might be?
 
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#2 ·
Now driving the same trip to work this morning it did great for 10 miles and then the temp started going up again, as soon as I came to the first light it dropped right back down and then stayed right around there for the rest of the trip.

Does this seem like a blown head gasket?
 
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#5 ·
Just made about a 20 mile trip with no issues, as soon as I pull into my driveway I noticed the temp going up. I shut it off opened the hood and it was pushing coolant out of the overflow bottle.

I feel like if the issue was the head gasket, it wouldn't drive fine for that long and then try to overheat.
 
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#7 ·
looks like you guys were right, I pulled one of the heads off last night and the gasket is def blown on that side. I over nighted OE replacement gasket set, new timing belt and pulleys, and a new water pump. Figured I might as well knock it all out while its taken apart.

I've changed many head gaskets, but never on a subaru. I was pleasantly surprised how simple this engine is to work on. Hopefully I will get it all back together by tomorrow.

Any tips or tricks to getting the timing belt on and timed correctly? Or is it just as simple as setting everything at TDC and putting the belt on then the tensioner? From what I have read, you just compress the tensioner slowly, lock it down, install, and then let it free. Anything wrong with this plan of action or is there a better way of doing it?
 
M
#8 ·
No, you do not set the crank at top dead center! You set it on the hash marks [not on the arrows] so that all the pistons are 1/2 way up. There are many, many U tubes. I must have watched 6-8 before doing mine. The DOHC is a little more difficult then shown on the SOHC U tubes of course.

 
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